In many applications a voltage regulator is required to provide a voltage within a predetermined range. Some circuits are subject to uncertain and undesirable functioning and even irreparable damage if an input power supply fall outside a certain range.
A prior art regulated power supply 600 is shown in FIG. 6. An input power converting circuit can include an AC generator 604 and a rectifier 607 coupled across an input Vin, a capacitor 605 also coupled across input Vin and coupled with a primary of transformer 610, a switch 608 coupled with the primary of the transformer 610 at a drain of the switch 608, and a pulse width modulator (PWM) module 606 coupled with a gate of the switch 608. The input power converting circuit can also include a rectifying diode 620 and capacitor 618 coupled across a secondary of the transformer 610. The power supply 600 can include a voltage regulating circuit including optical coupler circuit 612 and zener diode 622. The power supply 600 using the PWM module 606 to alter a duty cycle of the switch 608. The optical coupler circuit 612 in cooperation with zener diode 622 provides feedback to the PWM module 606. The PWM module 606 accordingly adjust the duty cycle of the switch 608 to compensate for any variances in an output voltage Vout of a load 623. A capacitor C1 also provides a substantial filtering to the power supply 600. However, the size of the capacitor C1 required for this type of power supply is prohibitively large.
Accordingly, it is desirable to create a regulated power supply to greatly reduce the size of the filter capacitor C1.